Method for treating coke oven gas

ABSTRACT

THE ELIMINATION OF ATMOSPHERIC POLLUTION RESULTING FROM SULFUR-CONTAINING TAIL GASES PRODUCED IN A HYDROGEN SULFIDE CONVERSION PROCESS ASSOCIATED WITH A COKE OVEN GAS BYPRODUCT RECOVERY SYSTEM IS DESCRIBED. THE SULFUR-CONTAINING COMPONENTS OF THE TAIL GAS ARE REMOVED BY FIRST COMBINING THE TAIL GAS WITH CRUDE COKE OVEN GAS IN THE BYPRODUCT RECOVERY SYSTEM. SULFUR DIOXIDE AND THE OTHER GASEOUS SULFUR-CONTAINING COMPONENTS OF THE TAIL GAS ARE REMOVED FROM THE COMBINED GASES BY THE VARIOUS GASTREATMENT PHASES OF THE BY-PRODUCT RECOVERY SYSTEM OR PASS THROUGH THE SYSTEM AND ARE SUBSEQUENTLY BURNED OR VENTED TO THE ATMOSPHERE AT LESS OBJECTIONABLE CONCENTRATIONS.

March 19, 1974 TATTERSQN 3,798,308

METHOD FOR TREATING COKE OVEN GAS Filed Jan. 19. 1972 United StatesPatent US. Cl. 423-574 7 Claims ABSTRACT OF THE DISCLOSURE Theelimination of atmospheric pollution resulting from sulfur-containingtail gases produced in a hydrogen sulfide conversion process associatedwith a coke oven gas byproduct recovery system is described. Thesulfur-containing components of the tail gas are removed by firstcombining the tail gas with crude coke oven gas in the byproductrecovery system. Sulfur dioxide and the other gaseous sulfur-containingcomponents of the tail gas are removed from the combined gases by thevarious gastreatment phases of the by-product recovery system or passthrough the system and are subsequently burned or vented to theatmosphere at less objectionable concentrations.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates generally to methods for eliminating the discharge ofobjectionable amounts of sulfur dioxide to the atmosphere. Moreparticularly the invention relates to methods for eliminating thedischarge of sulfur dioxide to the atmosphere from processes forproducing sulfur from the hydrogen sulfide recovered from crude cokeoven gas.

Prior art Crude coke oven gas produced during the carbonization of coalcontains components such as hydrogen, ammonia, hydrogen sulfide,naphthalene and other hydrocarbons that are normally removed from thecoke oven gas in a byproduct recovery, or gas treatment, system. Thepurified coke oven gas is thereafter sent to a gas distribution systemand is used as a fuel for the underfiring of coke ovens or as a fuel forvarious steel plant furnaces or for other industrial purposes.

The chemicals recovered from the crude coke oven gas are disposed of bya variety of methods. Ammonia, for example, may be disposed of simply byburning. Hydroden sulfide, on the other hand, is usually converted tovaluable by-products including sulfuric acid and elemental sulfur.

The processes for converting the hydrogen sulfide to sulfur usuallyproduce objectionable amounts of sulfur dioxide. One such process,conventionally termed the Clans Process, produces a tail gas containinglarge amounts of unconverted hydrogen sulfide, sulfur dioxide, and othersulfur-containing compounds that are generally incinerated anddischarged through a stack of sufiicient height to provide extremely lowsulfur dioxide concentrations at grade, or ground, level so as to complywith pollution codes. The incinerator and stack required for theincineration of the tail gas are major investment items. Efforts toreduce the incinerator and stack requirements and thus the initialprocess investment have heretoform been directed at increasing theefiiciency of the Claus Process.

SUMMARY OF THE INVENTION eliminates or at least minimizes therequirements of tail gas incinerator and exhaust stacks. Thesulfur-containing ICC tail gas is combined with crude coke oven gas inthe gas by-product recovery system. The sulfur dioxide and othersulfur-containing components react with the components of the coke ovengas or with the components of the solutions employed in the variousphases of the by-product recovery system and are removed from thecombined gases or pass through the by-product recovery system unchangedand are eventually burned or vented to the atmospheres at lessobjectionable concentrations.

The operation of the invention, however, can be better understood byreferring to the drawing and the description of the preferredembodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a schematic of a crudecoke oven byproduct recovery, or gas treatment, system which includesinter alia a cooling phase, a benzol washing phase and a hydrogensulfide absorption phase and of a process for converting hydrogensulfide to sulfur. The drawing illus trates the preferred embodiments ofthe invention.

For clarity purposes pumps, heat exchangers, valves and other ancillaryequipment not essential to a understanding of the invention have beeneliminated.

DETAILED DESCRIPTION Referring now to the drawing, there is illustrateda process for the removal of hydrogen sulfide from crude coke oven gasand for the conversion of the recovered hydrogen sulfide to elementalsulfur.

Crude coke oven gas produced during the carbonization of coal andcomprising ammonia, hydrogen sulfide, hydrogen cyanide, methane,hydrogen, naphthalene and other hydrocarbons flows through an initialcooling zone 1, which is generally a suction main, where it is cooledwith a spray of flushing liquor which, in addition to cooling the gas,absorbs a portion of the ammonia. The gas then flows into a separator 3where the flushing liquor and condensed tars are removed from the gasand flow through line 4 to flushing liquor decanter 17 where the tarssettle out and are removed through line 19. From the separator 3 the gaspasses through line 5 into a primary cooler 7 where it is further cooledand ammonia removed therefrom by means of a countercurrent flow of acooling liquor that enters the cooler 7 through line 9. The coolingliquor after cooling the crude gas ascending the cooler 7 is removedfrom the bottom of cooler 7 through line 11, cooled in heat exchanger 13and returned to the top of the cooler 7 through line 9. Excess coolingliquor resulting from the condensation of moisture contained in the cokeoven gas is removed from the cooler 7 through line 15 and passes toflushing liquor decanter 17. A portion of the flushing liquor fromdecanter 17 is returned through lines 21 and 23 to the initial coolingzone to contact another portion of crude coke oven gas. Excess flushingliquor, resulting from the condensation of the moisture contained in thecrude coke oven gas, is withdrawn from decanter 17 through line 21 andpasses to a crude liquor storage tank (not shown) through line 25 and iseventually passed to an ammonia still 27 where it is treated with eitherlime or caustic soda to free the combined ammonia. The freed ammonia isthereafter stripped from the liquor by means of stripping steam thatenters the still 27 through line 29. Stripped ammonia leaves still 27through line 31 and the stripped liquor leaves the still through line33.

From the primary cooler 7 the crude coke oven gas flows through line 35and is thereafter treated by processes (not shown) to remove tar,naphthalene, and the remaining portions of ammonia from the gas.Eventually the gas passes through line 37 into a benzol washing zone 39where the gas is contacted with a spray of washing solution, generallypetroleum wash oil, that enters the benzol washing zone 39 through line41 and that removes the so-called light oil from the gas. The petroleumwash oil containing the light oil, conventionally termed the benzolizedsolution, is removed from the bottom of the benzol washing zone 39through line 43 and is thereafter steam distilled (to remove the lightoil) and subsequently cooled before being returned to washing zone 39for contacting another quantity of the coke oven gas.

Following the removal of the light oil from the crude coke oven gas thegas passes through main 49 into a hydrogen sulfide absorption zone 51.Although the hydrogen sulfide may be removed from the coke oven gas byany known means, the Vacuum Carbonate Process is used in the preferredembodiments of the invention. In the Vacuum Carbonate Process analkaline metal carbonate solution, such as sodium carbonate, is employedto absorb hydrogen sulfide and other acid gases from the coke oven gasthereby forming a fouled solution. The fouled solution is thereafterheated under a vacuum to drive out the acid gases and to simultaneouslyregenerate the absorption solution.

In absorption zone 51 the coke oven gas is contacted with the alkalinemetal carbonate solution that enters the absorption zone 51 through line63. The alkaline metal carbonate solution absorbs the hydrogen sulfide(and other acid gases) from the gas and forms a fouled solution. Thenow-purified coke oven gas containing only residual amounts ofimpurities leaves absorption zone 51 through main 57 and is sent to agas distribution area (not shown) and is thereafter used as a fuel forthe underfiring of coke ovens or as a fuel in various steel plantfurnaces or for other industrial uses.

The fouled solution passes to an actification zone 55 through line 53where it is actified by stripping the hydrogen sulfide under vacuum bystripping steam that is generated from a portion of the actifiedsolution that is recirculated between actification zone 55 and heatexchanging means (not shown) through lines 56 and 59.

The portion of actified solution not recirculated is returned to the topof absorption zone 51 through lines 61 and 63, after first being cooledto absorption temperature in heat exchanger 65, to contact anotherportion of the coke oven gas.

As mentioned above, the removal of hydrogen sulfide by absorption withdilute alkaline metal carbonate solution, while preferred, is notessential to the invention and is used by way of illustration only. Itwill be understood by those skilled in the art that other means ofhydrogen sulfide removal may be used in the scope of this invention.Additionally, the removal of the light oil from the crude coke oven gasis not essential to the teachings of the invention and although used inaccordance with one of the preferred embodiments of the invention, maybe omitted depending on the chemical makeup of the crude coke oven gasand the purification requirements for a particular coke oveninstallation.

The hydrogen sulfide stripped from the fouled solution in actificationzone 55 and containing stripping vapor leaves actification zone 55through line 67 and is treated by some convenient means 69 (not shown)to remove the bulk of the stripping vapor.

The hydrogen sulfide gas then passes through line 70 to compressor 71and then through line 73 to a hydrogen sulfide conversion process 75which is, according to the preferred embodiments of the invention, theClaus Process.

The Claus Process converts hydrogen sulfide to an elemental form ofsulfur known as brimstone. In the process, hydrogen sulfide is burned inless than stoichiometric amounts of oxygen to convert a portion of thehydrogen sulfide to sulfur dioxide. The remaining portion of thehydrogen sulfide land the just-produced sulfur dioxide are thencatalytical'ly reacted to form sulfur and water and a tail gascontaining unconverted hydrogen sulfide, sulfur dioxide and othersulfuI-Gontaining compounds. The composition of a tail gas produced in atypical Claus Kiln Process is set out in Table I.

TABLE I Component: Tail gas (lbs. per hr.)

Hydrogen 5.72 Water vapor 1,089.00 Carbon monoxide 120.68 Nitrogen2,962.40 Oxygen None Carbon dioxide 344.96 Hydrogen sulfide 19.89

Sulfur dioxide 18.69

Carbonyl sulfide 13.14

Carbon disulfide 2.78

Sulfur vapors 3.50

The Claus Process is described in the preferred embodiments of theinvention since the problem of disposing of the sulfur-containing tailgas is very great with the Claus Process. The process of the invention,however, is applicable to other hydrogen sulfide conversion processesthat produce sulfur-containing tail gases.

tI-Ieretofore, in order to meet pollution standards, the tail gas from aClaus Process has been incinerated to convert the hydrogen sulfide andother sulfur-containing compounds to sulfur dioxide. The incinerated gasis vented to the atmosphere through large stacks so that the sulfurdioxide concentration at grade is within acceptable limits. To minimizeincinerator and stack requirements efforts have been aimed primarily atincreasing the efficiency of the Clans Process itself. Surprisingly, ithas been found that incinerator and stack requirements can be minimizedif not eliminated and the discharge of sulfur dioxide minimized oreliminated by combining the tail gas from the 3 Claus Process with thecrude coke oven gas in the byproduct recovery system in the mannerdescribed below. The unconverted hydrogen sulfide, sulfur dioxide, andother sulfur-containing compounds are neutralized by reaction with thecomponents of the coke oven gas or with the constituents of the variousgas-treatment solutions employed in the by-product recovery system. Aminor portion of the gases may pass through the gas purification systemunchanged and may be burned or vented to the atmosphere at less thanobjectionable concentrations.

Referring again to the drawing, hydrogen sulfide is converted inconversion process 75, which, as stated previously, is preferably aClaus Process, to sulfur (and Wa ter) and an unwanted sulfur-containingtail gas. The 5 sulfur is withdrawn from the convention process 75through line 77 and sent to a sulfur recovery area (not shown). The tailgas flows through line 79 and valve 81 to, in the particularly preferredembodiment, the initial cooling zone 1 before the separator 3 where thetail gas 5 is combined with the crude coke oven gas. The sulfur dioxidein the tail gas reacts with ammonia in the crude coke oven .gas in thepresence of the flushing liquor that is used to cool the gas to formaqueous ammonium sulfite that builds up in the flushing liquor. Theammonium 6 sulfite eventually passes to the decanter 17 with the excessflushing liquor and then to ammonia still 27. In ammonia still 27 theliquor is treated with, for example, lime or caustic soda to free theammonia contained in the liquor in the form of salts, which salts formduring the initial 65 cooling of the crude coke oven gas with theflushing liquor. The freed ammonia is then stripped from the liquor. Iflime is used to treat the liquor in the ammonia still the ammoniumsulfite reacts with the lime to form calcium sulfite, an insolubleprecipitate, which is dis- 7 charged from the still 27 with the stillbottoms through line 33. If caustic soda is used to treat the liquorsoluble sodium sulfite is produced which is also removed from the stillwith the still waste.

The sulfur vapors in the tail gas condense in the cooling zone 1 and areremoved from the combined gases along the flushing liquor and condensedtars in separator 3 and flow to flushing liquor decanter 17 and areremoved with the condensed tars through line 19.

Hydrogen sulfied in the tail gas flows with the crude coke oven gas andis eventually removed from the gas in the hydrogen sulfide absorptionzone.

The carbonyl sulfide in the tail gas is unstable and decomposes readilyto carbon monoxide and sulfur. The sulfur is removed in the separator 3as described above.

Carbon disulfide in the tail gas is neutral as to the components of thecrude coke oven gas and gas-treatment solutions and flows with the crudecoke oven gas through the primary cooler and other purification units tothe benzol washing zone 39 where it dissolves in the petroleum wash oil.The carbon disulfide is eventually removed from the by-product recoverysystem during purification of the petroleum Wash oil.

Water in the tail gas is condensed in the primary cooler and iseventually removed from the system as excess liquor.

The remaining components of the tail gas pass through the by-productrecovery system unchanged and flow with the treated gas to the gasdistribution system described above.

In a second embodiment of the disclosure, the tail gas flows throughlines 79 and 83 and 87 (shown in phantom lines) and valves 85 and 88(valve 81 is closed) and is combined with coke oven gas in line 37leading into benzol washing zone 39. It is desirable to cool the tailgas before discharging it into the line 37 so as to maintain a highabsorption rate of light oil. Sulfur vapors condensed in the tail gas,and sulfur resulting from decomposition of the carbonyl sulfide aredissolved in the petroleum wash oil and eventually removed from thebyproduct recovery system as described above. Hydrogen sulfide passesthrough the benzol Washing zone 39 and is removed in the hydrogensulfide absorption zone 51. Sulfur dioxide also passes to the hydrogensulfide absorption zone 51 and reacts with the alkaline metal carbonatesolution to form an alkaline metal sulfite which is removed from thesystem through line 89 with the waste liquor. This waste liquor can besent to the ammonia still 27 and the sulfite removed, after lime orcaustic treatment, from the system with the still bottoms.

As in the particularly preferred embodiment the small quantity ofcomponents of the tail gas inert to the gas purification system passthrough the system and are either burned or vented to the atmosphere.

In a third embodiment, the tail gas passes through lines 79 and 83 and91 (shown in phantom) and valves 85 and 93 (valves 81 and 88 are closed)into line 49 where it combines with the coke oven gas. In thisembodiment the tail gas is preferably cooled before discharging it intoline 49 so as to maintain a high degree of hydrogen sulfide absorptionin hydrogen sulfide absorption zone 51. The hydrogen sulfide from thetail gas is removed from the mixture of gases in the absorption zone 51as described above. The sulfur dioxide reacts with the alkaline metalcarbonate solution in the absorption zone 51 to produce an alkalinemetal sulfite which builds up in the solution until it is bled from thesystem through line 89 with objectionable Waste liquor. As in the secondembodiment the waste liquor may be passed to the ammonia still 27 andtreated with caustic or lime.

As an alternative to combining the tail gas with the coke oven gas atonly one of the three separate locations described above, it is possibleto apportion the tail gas and combine it with the coke oven gas at anytwo or all of the three locations.

Finally, it is posisb'le to contact the tail gas with an aqueoussolution of ammonia formed from ammonia recovered from the crude cokeoven gas. The ammonia and sulfur dioxide will react to form an ammoniumsulfite solution that can be passed to the ammonia still and treatedwith caustic soda or lime to form sodium sulfite or calcium sulfitewhich is thereafter removed from the still with the still bottoms asdescribed above. The tail gas may thereafter be sent to the gaspurification system as in the preferred embodiments or, if the amountsof other sulfur-containing compounds are low, may be vented to theatmosphere or may be combined with the purified coke oven gas and sentto a gas distribution system for use as a fuel.

Thus the invention enables the elimination of costly tail gasincinerators and stacks associated with sulfur recovery units andeliminates the discharge of large amounts of sulfur dioxide and othersulfur-containing compounds into the atmosphere by utilizing existingcoke oven gas purification processes and techniques.

It will be understood that the invention is not limited by theembodiments described. On the contrary, it is intended to cover allalternatives, modifications and equivalents that may be included withinthe spirit and scope of 20 the invention as defined by the appendedclaims.

In the claims:

1. In a process wherein crude coke oven gas formed during thecarbonization of coal and containing ammonia and hydrogen sulfide istreated to remove the hydrogen sulfide and wherein the so-removedhydrogen sulfide is further treated in a process that produces asulfur-containing tail gas including sulfur dioxide, the improvementcomprising: (1) combining the sulfur-containing tail gas with the crudecoke oven gas thereby neutralizing the sul- 0 fur dioxide with thecontained ammonia, and (2) thereafter subjecting the combined gases tothe gas treatment phases of said process including a benzol washingphase and hydrogen sulfide absorption phase.

2. In a process wherein crude coke oven gas that is produced during thecarbonization of coal and that contains ammonia and hydrogen sulfide iscontacted with an alkaline metal carbonate solution that removes thehydrogen sulfide from the gas to form a fouled hydrogensulfide-containing solution, said fouled hydrogen sulfide- 0 containingsolution thereafter being contacted with steam under vacuum conditionsto release the hydrogen sulfide from the solution, and wherein theso-released hydrogen sulfide is burned in less than stoichiometricamounts of oxygen to convert a portion of the hydrogen sulfide to sulfurdioxide, and the so-produced sulfur dioxide and unconverted hydrogensulfide thereafter catalytically reacted to produce elemental sulfur anda tail gas containing sulfur dioxide and other sulfur-containing gases,the im provement comprising:

combining the tail gas With the crude coke oven gas whereby the sulfurdioxide in the tail gas is neutra lized by the ammonia in the coke ovengas and the other sulfur-containing components of the tail gas areremoved from the combined gas in the process by selected proceduresincluding the steps of scrubbing with aqueous solutions and wash oil,treating with reactant chemicals, distilling and steam stripping.

3. In a process wherein crude coke oven gas formed during thecarbonization of coal, said gas comprising ammonia, hydrogen sulfide,light oil and other hydrocarbons, is purified in a by-product recoverysystem that comprises:

(a) an initial cooling zone wherein the gas is cooled with a spray offlushing liquor,

(b) a benzol washing zone wherein the gas is scrubbed with a petroleumWash oil to remove the light oil from the gas,

(0) a hydrogen sulfide absorption zone wherein the gas is scrubbed withan alkaline metal carbonate solution to form a fouled hydrogensulfide-containing solution, and

(d) an actification zone wherein the fouled hydrogen sulfide-containingsolution is contacted with steam under reduced pressure to free thehydrogen sulfide from the solution,

and wherein the freed hydrogen sulfide is:

(a) burned in less than stoichiometric amounts of oxygen to convert aportion of the hydrogen sulfide to sulfur dioxide, and

(b) the remaining portion of hydrogen sulfide is catalytically reactedwith the so-produced sulfur dioxide to form elemental sulfur and a tailgas containing residual amounts of hydrogen sulfide, sulfur dioxide andother sulfur-containing gases,

.the improvement comprising:

combining the so-produced tail gas with the crude coke oven gas in theinitial cooling zone of the by-product recovery system.

4. The process of claim 3 wherein the improvement comprises combiningthe so-produced tail gas with the crude coke oven gas in the benzolwashing zone.

5. The process of claim 3 wherein the improvement comprises combiningthe tail gas with the crude coke oven gas in the hydrogen sulfideabsorption zone.

6. A process for disposing of a sulfur dioxide-containing tail gas thatis generated by the catalytic conversion of hydrogen sulfide to sulfurin the Clans Process comprising combining the so-generated tail gas withcrude coke oven gas in the initial cooling zone of a coke oven UNITEDSTATES PATENTS 2,943,911 7/1960 Sweeney 423-550 1,961,255 6/1934 Sperr423550 2,200,529 5/1940 Baehr et a1. 423-576 1,043,211 11/1912 Doherty423-512 1,043,210 11/1'912 Doherty 423512 FOREIGN PATENTS 905,365 9/1962 Great Britain 423-574 OSCAR R. VERTIZ, Primary Examiner G. A.HELLER, Assistant Examiner U.S. Cl. X.R. 423237, 512, 242

